A percentage of semi-weathering slates, when exposed to the elements will change to brown, buff, and tan over time. The mineral and chemical composition of the slate contributes to the weathering process. As roofing slate is a natural product, the weathering can vary from quarry to quarry as well as the stone extracted from within a quarry. When ordering a “semi-weathering” slate it’s important to keep this in mind. The installer should also take the time to blend and sort from various pallets to avoid unsightly blotches of browns.
North Country Semi-Weathering (Vermont) Gray is a premium quality Vermont product with a rich battleship gray color that deepens over time. A percentage of this Vermont slate will weather to tones of brown and buff. These slate products make a popular roof covering alone or in combination with other slates to create a multi-colored roof. Produced by select Vermont quarries, North Country Semi-Weathering Gray slate meets or exceeds ASTM standards as an S-1 rated roofing slate.
In the slate industry, there are two color adjectives to explain color changes. “Semi-weathering” refers to the color changing over a course of time, whereas “unfading” refers to the slate maintaining its original color. If the slate tests as an ASTM S-1 rated roofing slate, both a semi-weathering and unfading slate will have the same durability and longevity. The decision on the color all comes down to the type of roof you want. For instance, you’ve narrowed down that you prefer gray colored slates. If you like the look of an “older” looking roof, you may want the Semi-Weathering Gray slate which will have a percentage of slates weather when exposed to the elements. If you want the slate roof to look the same as the day it was installed, you might prefer the Unfading Gray with is a light to medium gray with mottled inclusions of dark gray and black.